A feedback (closed-loop) control system 10, as shown in Prior Art FIG. 1, is widely used to modify the behavior of a physical process, denoted as the plant 110, so it behaves in a specific desirable way over time. For example, it may be desirable to maintain the speed of a car on a highway as close as possible to 60 miles per hour in spite of possible hills or adverse wind; or it may be desirable to have an aircraft follow a desired altitude, heading and velocity profile independently of wind gusts; or it may be desirable to have the temperature and pressure in a reactor vessel in a chemical process plant maintained at desired levels. All of these industrial tasks are accomplished today by using traditional feedback control, and the above are examples of what automatic control systems are designed to do, without human intervention.
The key component in a feedback control system is the controller 120, which determines the difference between the output “y” of the plant 110, (e.g., the temperature or position) and its desired value, and produces a corresponding control signal “u” (e.g., modulating the power input to a heater or motor).
The goal of controller design is to make the difference between the actual output of the plant and the desired output as small as possible as rapidly as possible. Today, controllers are employed in a large number of industrial control applications and in areas like robotics, aeronautics, astronautics, motors, motion control and thermal control, just to name a few.